plotly charts are described declaratively in the call signature of plotly::plot_ly, plotly::add_trace, and plotly::layout. Every aspect of a plotly chart (the colors, the grid-lines, the data, and so on) has a corresponding key in these call signatures. This page contains an extensive list of these attributes.

Plotly's graph description places attributes into two categories: traces (which describe a single series of data in a graph) and layout attributes that apply to the rest of the chart, like the title, xaxis, or annotations).

Here is a simple example of a plotly chart inlined with links to each attribute's reference section.

library(plotly)

p <- plot_ly(economics,
    type = "scatter",       # all "scatter" attributes: https://plot.ly/r/reference/#scatter
    x = date,               # more about scatter's "x": /r/reference/#scatter-x
    y = uempmed,            # more about scatter's "y": /r/reference/#scatter-y
    name = "unemployment",  # more about scatter's "name": /r/reference/#scatter-name
    marker = list(          # marker is a named list, valid keys: /r/reference/#scatter-marker
        color="rgb(16, 32, 77)"     # more about marker's "color" attribute: /r/reference/#scatter-marker-color
    ))

p <- add_trace(p,                       # by default, traces are type "scatter"
    y = fitted((loess(uempmed ~ as.numeric(date)))),  # scatter's "y": /r/reference/#scatter-y
    line = list(                        # line is a named list, valid keys: /r/reference/#scatter-line
        color = "rgb(60, 60, 60)",      # line's "color": /r/reference/#scatter-line-color
        dash = "dashed"                 # line's "dash" property: /r/reference/#scatter-line-dash
    )
)

maxdf <- dplyr::filter(uempmed == max(uempmed))

p <- layout(p,              # all of layout's properties: /r/reference/#layout
    title = "unemployment", # layout's title: /r/reference/#layout-title
    xaxis = list(           # layout's xaxis is a named list. List of valid keys: /r/reference/#layout-xaxis
        title = "time",     # xaxis's title: /r/reference/#layout-xaxis-title
        showgrid = F        # xaxis's showgrid: /r/reference/#layout-xaxis-showgrid
    ),
    yaxis = list(           # layout's yaxis is a named list. List of valid keys: /r/reference/#layout-yaxis
        title = "uidx"      # yaxis's title: /r/reference/#layout-yaxis-title
    ),
    annotations = list(         # all annotation properties: /r/reference/#layout-annotations
        list(
            x = maxdf$date,     # annotation's x: /r/reference/#layout-annotations-x
            y = maxdf$uempmed,  # annotation's y: /r/reference/#layout-annotations-y
            text = "Peak",      # annotation's text: /r/reference/#layout-annotations-text
            showarrow = T       # annotation's showarrow: /r/reference/#layout-annotations-showarrow
        )
    )
)